None of the following references, which were located by means of a search in the public records of the U.S. Patent and Trademark Office, shows a radar imaging system and an antenna suitable therefor, as in the present invention:
U.S. Pat. No. 3,673,606 discloses an array antenna using phase shifters. The antenna disclosed in the instant specification produces narrow beams at millimeter frequencies without using phase shifters.
U.S. Pat. No. 3,953,857 discloses a search and track directional antenna using phase shifters, which the present invention avoids.
U.S. Pat. No. 4,070,678 discloses an antenna mounted on a two-axis gimbal for steering beams through wide angles. The antenna of the present invention avoids bulky gimbals.
U.S. Pat. No. 4,203,113 discloses a radar system which can be used for an automobile application.
U.S. Pat. No. 4,297,708 discloses a system for correcting dispersion in a beam radiated by a flat microwave antenna due to variations in the frequency of operation by providing an electronically controlled phase shift of the beam in the plane of the dispersion.
Other references are U.S. Pat. Nos. 3,680,085; 3,821,736; and 3,878,525.